Interference mitigation and adaptive routing in wireless ad-hoc packet-switched networks

ABSTRACT

Described are an apparatus and method for routing packets through a multiple-hop wireless communications network. Interference with packet switched communications carried by radio frequency (RF) over the multiple-hop wireless communications network is detected. In response to information related to the detected interference, a route is adaptively determined for transmitting packets through the multiple-hop wireless communications network that mitigates the effect of the interference on the packets.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/029,378, filed Dec. 20, 2001, now U.S. Pat. No. 7,342,876 which isherein incorporated by reference in its entirety.

FIELD OF THE INVENTION

The invention generally relates to interference mitigation, and morespecifically to interference mitigation in wireless communicationsnetworks.

BACKGROUND OF THE INVENTION

As the popularity of wireless communication networks continues toincrease, a variety of protocols have emerged such as IEEE 802.11(a),IEEE 802.11(b), HOMERF, HYPERLAN and BLUETOOTH. Some of the protocolsoperate in the same band of the radio frequency spectrum, e.g.,802.11(b) and BLUETOOTH operate at 2.4 GHz. Consequently, if twonetworks are placed in close proximity to each other operating differentprotocols competing for the same radio frequency spectrum, thesenetworks may interfere with each other. Additionally, RF noise fromsources such as microwave ovens and cordless telephones, some of whichalso operate in the 2.4 GHz ISM frequency band, provide a hindrance tooverall network performance by introducing noise into the network.

Wireless ad-hoc networks, (i.e., networks without a central point ofcommunications) are subject to other forms of interference as well. Forexample, unauthorized users can gain access to the network and attemptto degrade network performance by flooding the network with traffic.

SUMMARY OF THE INVENTION

An objective of the invention is to provide a method and apparatus thatcan detect the presence of an interference source and adaptively controlcommunication between nodes in an attempt to mitigate the effects of theinterference.

In one aspect, the invention features a method for routing packetsthrough a multiple-hop wireless communications network. Interferencewith packet switched communications carried by radio frequency (RF) overthe multiple-hop wireless communications network is detected. A routefor transmitting packets through the multiple-hop wirelesscommunications network that mitigates the effect of the interference onthe packets is adaptively determined in response to information relatedto the detected interference.

The nodes of the network can operate according to one of the followingprotocols: IEEE 802.11; BLUETOOTH; HYPERLAN; or HOME RF. In oneembodiment, a source of the interference is identified to be a node inthe network and the adaptively determined route excludes the interferingnode. In another embodiment, one or more nodes within the network thatare affected by the interference are identified, and the adaptivelydetermined route excludes the interfered-with nodes. In yet anotherembodiment, a geographical location of a source of the interference canbe approximated, and the adaptively determined route excludes one ormore nodes near that location.

Interference can be detected by determining that signals received by anode are of an unauthorized protocol, that an address included in thesignals received by a node is from a known unauthorized user, or that aprotocol header included in signals received by a node has invalidinformation. The interference can be detected by a protocol operating ateither a physical layer or a data link layer of a protocol stack. Anetwork layer in the protocol stack can determine a route through thenetwork in response to a notification from either the physical or datalink layer.

In one embodiment, a protocol operating at a network layer of a protocolstack can detect suspicious communication behavior, and the detection ofinterference is confirmed by the physical layer in response to beingnotified by the network layer of the suspicious behavior.

Information related to the detecting of the interference is disseminatedto the nodes within the network. Such information can be an identityassociated with the source of the interference or the identity of a nodewithin the network that is being interfered with by the interference.

In another embodiment, an antenna pattern of a node in the network isadaptively adjusted in response to the detection of interference. A nullcan be formed in the antenna pattern in a direction of the interference.

In another aspect, the invention features a protocol stack used by anode to communicate over a wireless communications network. The protocolstack includes a radio frequency (RF) physical layer that detectssignals that are attempting to interfere with packet-switchedcommunications at the node and produces a signal that indicates thedetection of interference. A network layer receives the signal from thephysical layer and produces an alternate route of packets through thenetwork in response to the signal. In one embodiment, the protocol stackincludes a data link layer that detects signals that are attempting tointerfere with communications at the node and sends a signal to thenetwork layer indicating that interference has been detected.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is pointed out with particularity in the claims. Thedrawings are not necessarily to scale, emphasis instead generally beingplaced upon illustrating the principles of the invention. Like referencecharacters in the respective drawing figures indicate correspondingparts. The advantages of the invention described above, as well asfurther advantages of the invention, may be better understood byreference to the description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1A is a conceptual diagram of a mobile ad-hoc wirelesscommunications network;

FIG. 1B is a conceptual diagram of the mobile ad-hoc wirelesscommunications network in FIG. 1A after responding to a detectedinterfering node in accordance with the principles of the invention;

FIG. 1C is a conceptual diagram of the mobile ad-hoc wirelesscommunications network of FIG. 1A after responding to a link (non-nodesource) interference in accordance with the principles of the invention;

FIG. 2 is an embodiment of a protocol stack of the invention;

FIG. 3A is a block diagram of a first embodiment of a networkcommunications card;

FIG. 3B is a block diagram of a second embodiment of a networkcommunications card;

FIG. 4A is an embodiment of an antenna pattern produced by the firstembodiment of the network communications card;

FIG. 4B is an embodiment of an adaptive antenna pattern formed by thesecond embodiment of the network communications card; and

FIG. 5 is a flow diagram illustrating an embodiment of a process bywhich the nodes in the wireless communications network respond tointerference detected in the network.

DETAILED DESCRIPTION

FIG. 1A shows an embodiment of a multiple hop (multi-hop) wirelesscommunications network 100 constructed in accordance with the principlesof the invention. The network 100 is a packet-switched network in whichmessages are divided into packets that are transmitted individually overthe network 100 and reassembled at their destination to produce themessage. The network 100 includes a plurality of computing (orelectronic) devices 104 in communication with each other over a sharedmedium to form a wireless local area network (WLAN). In a shared medium,all computing devices 104 within range of a transmitted communicationcan hear that communication. In one embodiment, an effective range ofcommunication between computing devices 104 is approximately 150 to 200feet, which is typically referred to as “short range.” The paths ofcommunication between computing devices 104 that are withincommunication range of each other are represented by communication links112.

Generally, the computing devices 104 are battery-operated, portabledevices capable of wireless communication (e.g., shared medium radiofrequency (RF)). Examples of such computing devices 104 include but arenot limited to personal digital assistants (PDA), tablet-based andlaptop computers, calculators, mobile phones, handheld gaming devices,and picoradios.

Because such computing devices 104 are typically portable and havewireless communication capabilities, their users can move about freelyand remain part of the network 100. Further, the users are able tocommunicate with each other without their communications flowing througha central hub. Networks that operate without a fixed infrastructure(such as a coordinating central hub) are conventionally designated “adhoc.” Consequently, the wireless data communication network 100, ofwhich such computing devices 104 are a part, is generally referred to asa wireless mobile ad-hoc network.

To communicate over the network 100, each computing device 104 has ashared-medium wireless networking transceiver (e.g., IEEE Standard802.11). The capability to communicate over a shared medium is typicallyadded to the computing device 104 in the form of a networkcommunications card (or, generally, a shared-medium transceiver). Theshared-medium transceiver has antennae for communicating with thetransceivers of other computing devices 104 in the network 100 and, forsome embodiments, with a wireless access point 120. In general, thewireless access point 120 is connected to a wired network (not shown)and has a shared medium wireless networking transceiver, typically inthe form of a plug in card. The wireless access point 120 serves as ashared RF wireless transceiver for electronic resources, electronicdevices, and other access points connected by wire (e.g., cable) to thewired network.

In the network 100, the state of the communication links 112 (i.e., linkstate) between computing devices 104 (hereafter referred to as nodes104) can change frequently because the nodes 104 are mobile. One or moreof the nodes 104 may move from one location to another location,dynamically breaking existing links 112 and establishing new links 112with other nodes 104 as a result. Such movement by one node 104 may notnecessarily result in breaking a communication link 112, but maydiminish the quality of the communications with another node 104 overthat link. In this case, a cost of that link 112 has increased. Althoughdescribed in the context of a dynamically changing networkconfiguration, the principles of the invention apply also to staticnetwork configurations, in which no link-state changes occur due to nodemobility.

Each node 104 in the network 100 is responsible for detecting, updating,and reporting changes in cost and up-or-down status of each outgoingcommunication link 112 to neighbor nodes (i.e., nodes withincommunication range). In accordance with the principles of theinvention, each node 104 can detect a source that interferes withcommunication over the network 100, hereafter referred to as aninterfering or unintended source, inform other nodes 104 of theinterfering source, and appropriately adjust the packet routes throughthe network 100. Also, in one embodiment each node 104 runs a neighbordiscovery protocol for detecting the arrival and departure of neighbornodes and a link-state-routing protocol for disseminating networktopology and link-state information, such as information related to aninterfering source, to the other nodes 104 in the network 100.

FIGS. 1A-1C illustrate the principles of the invention in an exemplaryconfiguration of the network 100. Referring to FIG. 1A, consider that asource node (S) 104 has determined a route to a destination node (D) 104that takes multiple hops. This route between nodes S and D isillustrated by a thick outline that passes through intermediate nodes A,B, i.sub.1, and E. Each of the intermediate nodes A, B, I.sub.1, and Ereceiving a packet that originated from source S forwards the packet tothe next hop in the route towards the destination node D. For forwardingsuch packets, each intermediate node A, B, I.sub.1, and E can userouting tables.

In the example shown in FIG. 1A, node I.sub.1 is an interfering nodethat interferes with the communications passing through node I.sub.1.This interference can take one or more of a variety of forms, and thusis generally viewed as behavior that unintentionally or intentionallyaffects a node's 104 ability to communicate over the network 100. Fromthe viewpoint of the node S 104, the interference can be of the typethat affects node S 104 directly. For example, the interfering nodeI.sub.1 can receive packets from node S 104, but not forward them. Theinterference can be of the type that affects node S indirectly byjamming the ability of one or more of the intermediate nodes (A, B, andE) to receive communication signals. The user of node I.sub.1 can createthis interference by deliberately emitting signals at an interferingfrequency or by executing a denial of service attack by pushing a largeamount of traffic. In accordance with the principles of the invention,each node 104 within range can detect the interfering node I.sub.1 anddisseminate information about the interfering node I.sub.1 through thenetwork 100. Each of such nodes 104 can also create a null in theantenna pattern toward the interfering node I.sub.1 104 to mitigate theeffects of the interference on that node 104. Further, the nodes 104 canadapt their packet routes to bypass the interfering node I.sub.1.

FIG. 1B illustrates a behavior of the exemplary network 100 in thepresence of the interfering node I.sub.1. In this example, consider thatnodes A, B, C, E, F, and H each detect the interference generated by theinterfering node I.sub.l. Each of such nodes A, B, C, E, F, and H 104create a null in the antenna pattern toward the interfering node I.sub.1104, and adapt their routing tables to produce routes that avoidinterfering node I.sub.1. The interfered-with nodes A, B, C, E, F, and H104 also disseminate information about the interfering node I.sub.1 sothat other nodes that do not detect the interference directly, such asnode S 104, can produce a new route through the network 100 to thedestination node (D) 104. An example of such a new route from sourcenode S to destination node D, which avoids passing through theinterfering node I.sub.1, is shown in thick-highlight in FIG. 1B aspassing through intermediate nodes A, B, F, and E.

Interference may originate from a source that is not a node in thenetwork 100. Unintentional jamming can result from appliances such as acordless telephone or a microwave that emits signals in the frequencyrange used by the nodes 104 to communicate. Another non-node source ofinterference can be from another computing device 104 that operates atthe same communication frequency but according to a different protocol,such as occurs between BLUETOOTH and IEEE 802.11.

Referring back to FIG. 1A, a non-node source of interference (denotedI.sub.2 108) is within sufficient proximity of nodes A, B, and C tocause interference with communications to, from, and through these nodesA, B, and C. Each node A, B, and C detects the interfering sourceI.sub.2 108, notifies other nodes 104 of the interfering source I.sub.2108, and adaptively determines at least one route for packets throughthe network 100 that avoids the interfering source I.sub.2 108. Newroutes can also avoid nodes that are being interfered with. Further,each of these nodes A, B, and C can create a null in the antenna patterntoward the interfering source I.sub.2 108 to mitigate the effects of theinterference on the network 100. An advantage achieved by the adaptiverouting is that, unlike a network with a central hub, such as a networkof wireless computing devices communicating through one access point,there is no single point of failure. The adaptive routing enables thecomputing devices to maintain connectivity in the RF dense metropolitansand in the presence of malicious jammers. Generally, a jammer is one whodeliberately uses electronic measures that radiate, reradiate, orreflect electromagnetic energy for the purpose of disrupting use of theelectronic computing devices, equipment, or systems.

From the information disseminated over the network 100 by the nodes A,B, and C, the source node S 104 can determine a new route through thenetwork 100 to the destination node (D) 104 that avoids each of theseinterfered-with nodes. FIG. 1C shows in thick highlight one suchexemplary route from the source node (S) to the destination node (D)through intermediate nodes G, H, and E, avoiding nodes A, B, and C whichare potentially being interfered with.

Network communication among the nodes 104 (and wireless access points120) is generally conceptualized in terms of protocol layers, such asthe physical, data link, network, and application layers, and suchprotocol layers form a protocol stack. In general, the protocol layersexchange control and status information with one another. For a node 104transmitting a communication, control starts at the application layerand passes layer by layer to the physical layer, which sends thecommunication over a communication link to a receiving node 104. Thereceiving node 104 processes the communication, layer by layer, up thestack of protocol layers, starting at the physical layer and ending atthe application layer.

FIG. 2 shows one embodiment of a simplified protocol stack 200 by whichthe nodes 104 communicate with each other to implement thepacket-switched network 100. Protocols that implement a packet-switchednetwork divide messages into packets before the messages are sent. Eachpacket contains the source and destination addresses and the data. Eachpacket is then transmitted individually and can follow different routesto its destination. The original message is recompiled at thedestination after all the packets forming the message arrive.

The simplified protocol stack 200 includes a physical layer 204, datalink layer 208, network layer 212, and application layer 212. It is tobe understood that the protocol stack 200 can have additional protocollayers to those shown, such as a transport layer, and still practice theprinciples of the invention.

The protocol used at the physical layer 204 of the protocol stack 200accommodates the type of physical medium over which the nodes 104communicate. The physical layer 204 conveys the bit stream in the radiosignal through the network 100 at the electrical and mechanical level,and provides the hardware means of sending and receiving data.

In one embodiment, the nodes 104 communicate with each other over links112 using an IEEE 802.11 wireless communications standard (e.g., IEEE802.11(a), IEEE 802.11(b), and IEEE 802.11(g)). Other embodiments ofwireless communications standards that can be used by the nodes 104include BLUETOOTH, HYPERLAN, and HomeRF. For a node 104 operatingaccording to the IEEE 802.11, the physical layer 204 specifies thephysical aspects of the radio signaling (e.g., frequency hopping spreadspectrum (FHSS), and direct sequence spread spectrum (DSSS)). Currently,an IEEE 802.11(b) node using DSSS can operate at up to speeds of 11 Mbpsin the 2.4-GHz to 2.4835-GHz spectrum. The data link layer 208 encodesand decodes data packets into bits and handles errors in the physicallayer 204, flow control and frame synchronization. In one embodiment,the data link layer 208 comprises two sub-layers: a Logical Link Control(LLC) layer and a Media Access Control (MAC) layer (the lower of the twosub-layers). The MAC sub-layer controls access to the physicaltransmission medium; the LLC layer controls frame synchronization, flowcontrol, and error checking.

For a node 104 operating according to the IEEE 802.11, the MAC layersupports a variation of Carrier Sense Multiple Access with CollisionAvoidance (CSMA/CA) with positive acknowledge. When a node 104 wants totransmit, the node 104 first checks the shared medium to see if themedium is free. If the shared medium is free, then the node 104 ispermitted to transmit. The node 104 receiving the transmissiondispatches an acknowledgment to inform the transmitting node 104 stationthat a collision did not occur. If the transmitting node 104 does notreceive an acknowledgment packet, the transmitting node 104 resends thepacket.

To minimize collisions due to nodes that do not hear each other, theIEEE 802.11 standard defines a virtual-carrier sense mechanism.According to this mechanism, the transmitting node 104 first sends aRequest to Send (RTS), which is a short packet that contains the sourceand destination addresses, and the duration of the transmission. Afterreceiving the RTS packet, the receiving node 104 replies with a shortpacket called Clear to Send (CTS), which includes the sameduration-of-transmission information. Nodes that receive the RTS, CTS,or both RTS and CTS packets then consider the medium busy for thatduration. Thus, the possibility of collisions in the medium is reduced.

The network (or routing) layer 212 provides a protocol for forwardingand routing packets through the network 100, by creating logical pathsfor transmitting packets from node to node.

Interference Detection

During operation of the network 100, each of the physical 204, data link208 and network layers 212 participate in the detection of interferencein the network 100. An advantage of the invention is that nodes 104 areable to detect the interference at those protocol layers closer to thesource of the problems, namely the lowest layers 204, 208, 212 of theprotocol stack 200. At the lowest layer, such as at the physical layer204, it is possible to separate the interfering signal from the actualsignal.

The physical layer 204 can detect interference in one or more ways. Ingeneral, software that implements the physical layer protocol examinesheader information of the packets received over the shared medium. Suchheader information is typically intended for use by the higher protocollayers of the protocol stack 200. In one embodiment, the physical layer204 examines the header information of received packets to determine ifthe packets follow a particular expected protocol. For example, if thenode 104 is operating according to the 802.11 standard, and receivedpackets do not have the appropriate frame format, then the physicallayer 204 can conclude that the node's 104 communications are beinginterfered with. The physical layer 204 can employ threshold criteriabefore reaching this conclusion, such as strength of receivedinterference and duration of interference.

In another embodiment, the physical layer 204 examines the headerinformation to determine an address of the source of the packet (“sourceaddress”). The source address can be a MAC address or an IP address ofthe node transmitting the packet. The software operating at the physicallayer 204 can then compare the source address with a list of knownunauthorized nodes. If the source address is listed therein, then thesource of the packet is an interfering node. Conversely, the physicallayer software can compare the source address with a list of knownauthorized nodes. If the source address is not found in that list, thesource of the packet is identified as an interfering source.

Upon detecting interference, the physical layer 204 notifies the networklayer 212, so that the network layer 212 can act accordingly (e.g.,adapt packet routes in response to the interference). As an example, thephysical layer 204 can accomplish this notification by setting orunsetting a bit in one of the header fields, which is subsequentlyexamined by network layer software. The physical layer 204 can alsocontrol transceiver operation (described below), in response todetection of the interference, to mitigate the effects of theinterfering signals on the communication of the node 104. In oneembodiment, the physical layer 204 tests periodically if the interferingbehavior from the interfering source has ceased by restoring thereception and transmission antenna pattern to its previouspre-interference state. If so, the physical layer 204 notifies thenetwork layer 212 of the change of state, and the network layer 212adapts its packet routes accordingly.

At the data link layer 208, software can examine the information fieldsof RTS and CTS packets to determine if the node 104 is receiving falseRTS or CTS packets or a flood of RTS/CTS packets. For example, each RTSpacket has information fields for a receiver address and a transmitteraddress and each CTS packet has an information field for a receiveraddress that the data link software can compare against a list ofauthorized (or unauthorized) addresses. These fields store the MACaddress of the transmitting or receiving device. If any of the addressesare invalid (i.e., not a proper MAC address) or on a list ofunauthorized addresses (or not on a list of authorized addresses), thenthe data link layer 208 can conclude that the sender of the packet (RTSor CTS) is an interfering source. As with the physical layer 204, thedata link layer 208 can employ threshold criteria to determine if thereceipt of the invalid or unauthorized RTS or CTS packet rises to thelevel of interference.

As another example, the data link layer software can examine theduration field, which is part of both RTS and CTS packets, to determineif a valid duration is being used. An invalid duration (e.g., one ofexcessive duration or a CTS duration that does not match a correspondingRTS duration) can be an indicator of a node attempting to interfere withnetwork communications.

Upon detecting interference, the data link layer 208 notifies thenetwork layer 212. As an example, the data link layer 208 can notify thenetwork layer 212 by setting or unsetting a bit in one of the headerfields associated with the received packet, which is subsequentlyexamined by network layer software.

At the network layer 212, software can perform traffic analysis toidentify various types of attacks. For example, by examining the addressfield of packet traffic the network layer 212 can determine whetherexcessive traffic is originating from a particular node in the network100. As another example, using traffic analysis the network layer 212can detect another type of suspicious network behavior, such as when aninterfering node is receiving but not forwarding packets. This type ofsuspicious behavior can be detected, for example, when a higher protocollayers such as the transport layer retransmits packets because thedestination node never received the original packet.

In the event of detecting suspicious behavior, the network layer 212 cancommunicate with the physical layer 204 to confirm, if possible, thatthe suspect node is in fact behaving maliciously. If the physical layer204 confirms the malicious behavior, then the physical layer 204communicates this result to the network layer 212, and can alter thetransceiver reception and transmission patterns to avoid communicationsto, from, and through that malicious node.

When notified of interference, whether by the physical layer 204 or bythe data link layer 208, software operating at the network layer 212determines one or more routes through the network 100 that bypass aninterfering node producing the interfering signals or nodes that arebeing interfered with. Such a determination of routes can also be basedon messages received from other nodes in the network 100 that have alsodetected the interference. In one embodiment, the determination ofroutes is achieved by dropping existing routes that include theinterfering node, by dropping routes that include interfered-with nodes,or by dropping route that include both. The node 104 subsequently usesthose routes through the network 100 that remain.

As an example, the determination of routes involves establishing newroutes through the network 100 by calculating a cost for a plurality ofroutes that exclude the interfering node. A best route can then beselected based on route cost. In general, link cost can be calculated byone of a variety of cost functions. For example, one cost function caninclude the number of hops that a neighbor node is away from thedestination node; the further away from the destination node, the higherthe link cost for transmitting a packet to that node. As furtherexamples, a cost function can include congestion or bandwidthinformation over particular links 112 or at particular nodes 104—themore congested or the lower the bandwidth, the higher the cost toforward packets over those links 104 or through those node s104.

As yet another example, the nodes 104 can employ a cost function thatincludes calculating the power consumption information for thetransmitting node. For example, the transmitting node can haveaccumulated link-state information that shows that less power is neededto transmit a packet to one neighbor node than to another neighbor node.Accordingly, the best route is the route that consumes less power. Thispower calculation need not correlate with distance. For instance, atransmitting node may have one neighbor node that is geographicallynearer than another neighbor node, but behind an obstacle thatnegatively affects the signal quality, and therefore requires greaterpower to communicate therewith.

As another embodiment, the network layer 212 can divide packets andredundant checksums over disjoint paths that lead to the destinationnode. Disjoint paths are separate paths that have only the source anddestination nodes in common; that is, no intermediate node appears ineach path. For example, in FIG. 1A there are three disjoint paths fromthe source node S 104 to the destination node D 104. A first pathtraverses nodes S, A, B, F, L, and D; a second path traverses nodes S,C, I.sub.1, E and D; and a third path traverses nodes S, G, H, K, J, andD. The network layer 212 operates to send one packet over a first path,a second packet over a second path, and checksums over a third path.This prevents an interfering node (e.g., node I.sub.1) that isintermediate between the source and destination nodes from viewing allof the packets. Further, attempts to modify the data by the interferingnode should not escape detection. Also, data lost on any one path can berecovered by the information obtained along the other paths.

At the physical layer 204 of the protocol stack 200 is a networkcommunications card that transmits and receives information for thenodes 104. FIG. 3A shows one embodiment of a network communications card300 that is added to the nodes 104 to provide wireless communicationscapability. The network communications card 300 includes two antennaelements 304 a and 304 b, referred to generally as 304, a switch 308, acontroller 312, and a receiver 316. Antenna elements 304 are incommunication with switch 308. Switch 308 is in communication with andcontrolled by controller 312. Only one of the antenna elements 304 isconnected to receiver 316 at one specific time.

In operation, a single antenna element 304 is selected in response tocontrol signal SCONTROL generated by controller 312. Switch 308 connectsone of the antenna elements 304 to receiver 316 in response to adetermination of the quality of reception of each antenna element 304relative to each other. As the configuration of the mobile ad-hocnetwork 100 changes or reception quality falls below a threshold, switch312 is connected to the one of the antenna element 304 which provides anappropriate level of signal reception. Accordingly, when an interferingsource is detected, as described below, the controller 312 causes theswitch 312 to select the antenna that is less affected by theinterference.

FIG. 3B shows another embodiment of a network communications card 300′that provides wireless communications capability to the nodes 104.Network communications card 300′ includes antenna elements 304 a and 304b, referred to generally as 304, low noise amplifiers (LNA) 306 a and306 b, referred to generally as 306, receiver 316, a vector modulator320, a summer 340 and a controller 344. Antenna element 304 a is incommunication with low noise amplifier 306 a, which is in communicationwith vector modulator 320. Antenna element 304 b is in communicationwith low noise amplifier 306 b. Vector modulator 320 and low noiseamplifier 306 b are in communication with RF summer 340. The low noiseamplifiers 306 ab maintains a high quality received signal may need tobe inserted in the paths leading from antenna element 304 a to the RFsummer 340. This low noise amplifier 306 a overcomes the signal loss ofthe in-line vector modulator 320, which would degrade the receiver noisefloor. In order to provide signal level balance the low noise amplifier306 a is paired with the low noise amplifier 306 b in path from theantenna element 304 b to the RF summer 340. These low noise amplifiers306 replace a front-end amplifier within the receiver 316. Controller344 is in communication with vector modulator 320. Receiver 316 receivesthe output of summer 340 and is in communication with controller 344.

In such an embodiment, antenna elements 304 a and 304 b function as atwo-element (i.e., dual) antenna array. As such, the directionality ofthe transmit and receive patterns of the dual-antenna array can beexploited by the controller 344 in various ways (other than to mitigateinterference or to avoid communicating through an interfering node). Forexample, the directionality and shape of the antenna patterns can beadapted to achieve noise reduction and to improve the signal-to-noise(SNR) ratio of communications between nodes 104. Additional advantagescan be realized by such an implementation without departing from thespirit and scope of the invention.

In one embodiment, vector modulator 320 includes a signal splitter and a90.degree. phase shifter. 324, an in-phase amplitude control (I control)328, a quadrature-phase amplitude control (Q control) 332, and a signalcombiner and 0.degree. phase shifter 336. Signal splitter and 90.degree.phase shifter 324 are in communication with antenna element 304 a. Icontrol 328 and Q control 332 are in communication with signal combinerand 0.degree. phase shifter 336 as well as controller 344. Signalcombiner and 0.degree. phase shifter 336 are in communication withsummer 340.

In operation, antenna elements 304 receive and transmit informationpackets over the mobile ad-hoc network 100. The received signals areprocessed to determine if an interference source is withincommunications range of the receiving node. In response, controller 344adjusts I control 328 and Q control 332 using control signals ICONTROLand QCONTROL respectively.

In one embodiment, ICONTROL and QCONTROL are generated external to thevector modulator 320. In one embodiment, ICONTROL and QCONTROL aregenerated by a digital-to-analog (D/A) converter within controller 344,with one D/A for I control 328 and one D/A for Q control 332. Controlsignals ICONTROL and QCONTROL may be adaptive. For adaptive adjustmentof I control 328 and Q control 332, the controller 344 monitors theoutput of receiver 316. The output is used to determine the quality ofthe signal input to receiver 316, such as the received signal to noiseratio or the recovered bit error rate of the received signal. Thesefactors are in turn used to determine the presence of an unintended(interfering) signal source, for example, a microwave oven or a cordlesstelephone. Controller 344 adjusts the I control 328 and Q control 332signals ICONTROL and QCONTROL via an algorithm implemented in softwareto adaptively mitigate the effects of the interfering signal.

As signals pass through the vector modulator 320, the phase andamplitude of the desired received signals and the interfering signal arevaried. The signals from the I and Q signal paths are combined by the 0degree phase shift signal combiner 336 and pass through to the summer340. At this point, the signals from antenna element 304 b and the I andQ signal paths are combined at a summer 340.

In general, the relative phase of the desired signal and interferingsignals is different in the unweighted and weighted signal paths, due tothe differing distances of the signal sources to each antenna element.If the interfering signal is adjusted to be opposite in phase but at thesame amplitude in the weighted path relative to the unweighted path, theinterfering signal will cancel, and an improvement in signal tointerference ratio results.

In essence, the vector modulator 320 functions as a variable phase andamplitude network. By adjusting the phase of a desired signal and thatof at least one interfering signal received by antenna element 304 arelative to the desired signal and the at least one interfering signalreceived by the antenna element 304 b, the spatial direction of theradiation pattern null of network communications card 300 is changed.Therefore, there is a range of control settings on the I and Q signalpaths of vector modulator 320 that produces a reduction of interferencefor a bandwidth segment at receiver 316. For example, if the vectormodulator 320 controls are set such that no signal is available at theoutput of the vector modulator 320, then the interference is notdecreased. However, if the control setting is such as to steer theradiation pattern null of network communications card 300 towardsinterfering source or node, then the interference is noticeably reduced.

In one embodiment, in order to ascertain that an interfering signalstill exists, the physical layer 204 listens at a low duty cycle to thelink 212 without nulling being enabled. This snapshot of data is used tocharacterize the signal environment to determine if the interferer isstill present, and thus if the null should be formed in that direction.Otherwise, the radiation pattern null is disabled, allowing for signalreception in the direction of the former interferer.

By way of example, FIG. 4A shows the antenna pattern 400 of theembodiment of the network communications card 300 of FIG. 3A. Switchingbetween like antenna elements 304 a and 304 b affects a relativedirection of the receive antenna pattern 400 a, but does not alter theshape of the pattern.

FIG. 4B depicts a receive antenna pattern 400 b for the embodiment ofthe network communications card 300′ of FIG. 3B. In response to thecontroller 344 adjusting the I 328 and Q 332 control, a null 404 formsin the antenna pattern 400 b in the direction of an unintended(interfering) signal source. As the configuration of mobile ad-hocnetwork 100 changes and new interference sources are determined, thenull of the antenna pattern is shifted to form in the direction of thedetected interference source.

FIG. 5 shows an embodiment of a process 500 by which each node 104 inthe network 100 detects an interfering source and adaptively routespackets through the network 100 in response to detecting the interferingsource. For illustration purposes, although described from the viewpointof the node B 104 in the exemplary network 100 shown in FIG. 1A, it isto be noted that the process 500 is performed by each node 104 and, insome embodiments, each wireless access point 120 in the network 100.

In step 504, node B detects interference with its communication over thenetwork 100. Node B can detect the interference at the physical layer204, the data link layer 208, or the network layer 212, depending uponthe type of interference being encountered. For example, the physicallayer 204 detects jamming as described above, the data link layer 208detects hogging of resources such as occur during denial of serviceattacks, and the network layer 212 detects network behavior anomalies,such as packets not forwarded.

In step 508, node B determines information about the interfering source.In one embodiment, this information can be the name or otheridentification, such as Internet Protocol (IP) address or Media AccessControl (MAC), of the interfering node. In another embodiment, theinformation is related to a geographical location of the interferingsource. For example, the transceiver of node B can determine directionand distance of the interfering source from the signals received by theantennae. As another example, the node B can approximate the location(e.g., using triangulation techniques) from direction and distanceinformation received from two or more other nodes 104 in the network 100that have also detected the presence of the interfering source.

In step 512, node B can optionally adjust the antenna pattern, asdescribed above, such that the effects of the interference on receivedcommunications are mitigated.

In step 516, node B adapts its routes through the network 100 fortransmitting packets. In one embodiment, if the interfering source is anode 104 in the network 100 (e.g., node I in FIG. 1A), node B can dropany routes that include that node. In another embodiment, node B candrop routes with nodes that have been identified as being interferedwith. Also, the transceiver of node B can adjust the antenna pattern tocontrol the direction of transmitted communications so that theinterfering node or interfered-with nodes do not receive any packetsoriginating from or forwarded by node B.

In step 520, node B communicates to other nodes 104 in the network 100that the interfering source has been detected. This communication caninclude such information as described above, namely an identification ofor location of the interfering source. The communication can alsoinclude a flag that indicates whether node B is being interfered with.The direction of the transmission can be controlled, as described above,to keep the interfering node from receiving this communication and thusfrom recognizing that it has been detected.

While the invention has been shown and described with reference tospecific preferred embodiments, it should be understood by those skilledin the art that various changes in form and detail may be made thereinwithout departing from the spirit and scope of the invention as definedby the following claims.

1. A method for use by a node to route packet traffic through amultiple-hop wireless communications network, the method comprising:detecting an interference in a form of signals that are attempting tointerfere with packet-switched communications at the node that arecarried by radio frequency (RF) over the multiple-hop wirelesscommunications network; determining, in response to information relatedto the detected interference, a route for transmitting packets throughthe multiple-hop wireless communications network that mitigates aneffect of interference on the packets; and disseminating to other nodesin the multiple-hop wireless communications network an identity of atleast one node associated with the interference.
 2. The method of claim1 further comprising identifying a source of the interference to be afirst node in the multiple-hop wireless communications network, andwherein the determined route excludes the first node.
 3. The method ofclaim 1 further comprising identifying one or more nodes interfered withby the interference, and wherein the determined route excludes the oneor more of the interfered-with nodes.
 4. The method of claim 1 furthercomprising approximating a geographical location of a source of theinterference, and wherein the determined route excludes one or morenodes near that geographical location.
 5. The method of claim 1 whereinthe detecting the interference includes determining that signalsreceived by a node are of an unauthorized protocol.
 6. The method ofclaim 1 wherein the detecting the interference includes determining thatan address included in signals received by a node is an address of aknown unauthorized source.
 7. The method of claim 1 wherein thedetecting the interference includes determining that a protocol headerincluded in signals received by a node has invalid information.
 8. Themethod of claim 1 further comprising operating a protocol at a physicallayer of a protocol stack that detects the interference.
 9. The methodof claim 8 wherein the determining the route is performed by a networklayer protocol in the protocol stack in response to a notification fromthe protocol of the physical layer of the interference.
 10. The methodof claim 1 further comprising operating a protocol at a data link layerof a protocol stack that detects the interference.
 11. The method ofclaim 10 wherein the determining the route is performed by a networklayer protocol in the protocol stack in response to a notification fromthe protocol of the data link layer of the interference.
 12. The methodof claim 1 further comprising operating a protocol at a network layer ofa protocol stack that detects suspicious communication behavior.
 13. Themethod of claim 12 wherein the detecting the interference isaccomplished by a physical layer protocol of the protocol stack inresponse to a notification from the protocol of the network layer of thesuspicious network behavior.
 14. The method of claim 1 furthercomprising adjusting an antenna pattern of a node in the multiple-hopwireless communications network in response to detecting theinterference.
 15. The method of claim 14 wherein the adjusting theantenna pattern includes forming a null in the antenna pattern in adirection of the interference.
 16. The method of claim 1 wherein theidentity identifies a source of the interference.
 17. The method ofclaim 1 wherein the identity identifies a node in the multiple-hopwireless communications network that is being interfered with by theinterference.
 18. The method of claim 1 further comprising identifying asource of the interference to be a node in the multiple-hop wirelesscommunications network, calculating a cost function for a plurality ofroutes from a sending node to a destination node that exclude theinterfering node, and selecting the route with a lowest cost function.19. The method of claim 1 wherein nodes in the multiple-hop wirelesscommunications network operate according to one of protocols selectedfrom a group comprising of: IEEE 802.11, BLUETOOTH, HYPERLAN and HOMERF.20. A method for use by a node to route packet traffic through amultiple-hop wireless communications network, the method comprising:detecting an interference in a form of signals that are attempting tointerfere with packet-switched communications at the node that arecarried by radio frequency (RF) over the multiple-hop wirelesscommunications network, wherein the detecting is performed by a protocoloperating at at least one of: a physical layer of a protocol stack, adata link layer of the protocol stack, or a network layer of theprotocol stack; and determining, in response to information related tothe detected interference, a route for transmitting packets through themultiple-hop wireless communications network that mitigates an effect ofinterference on the packets.